Structure elucidation and conformational analysis of a fused cyclopentanopyrazolidinol

Abstract

From the reaction of 2-acetylcyclopentanone with benzoylhydrazine, the cyclopentanopyrazole derivative 4 was obtained as the only product. The structural assignment of this compound and also of the hydroxypyrazoline 3, used as a model compound, was established by analysis of their NMR spectra ( 1 H, 13 C, COSY, NOESY, HETCOR and COLOC).

Chemoselectivity and Conformational Analysis of the Reaction of 2‐Acetylcycloalkanones with Benzohydrazide: Synthesis and Reduction of 1‐Aroylcycloalkapyrazole Derivatives

“…Moreover, the quaternary C-atom at 161.1 ppm correlates with the H-atoms at d 2.61 ± 2.70 and 1.90 ± 2.10 and/or 1.88 ± 2.05. The chemical shift of the Me C-atom at 27.4 ppm is quite different from that observed for the Me C-atom (14.8 ppm) of compound 2a, but is in better agreement [9] with the MeÀC(5) chemical shift (21.7 ppm) of compound 4. In addition, the hydroxylated Catom resonates at 91.6 ppm, a value that is closer to the one observed for C(5) (95.2 ppm) of compound 4 instead to that for C(6a) (103.0 ppm) of compound 2a.…”

“…Since, from the studied reaction, two possible OH isomers 2a and 3a can be formed, the structure of the isolated OH derivative was elucidated in connection with the spectral data of the known [8] 4,5-dihydro-5-hydroxy-3,4,4,5-tetramethyl-1-(4-methylbenzoyl)-1H-pyrazole (4) (Scheme 1). To the derived OH isomer, the structure of 1-benzoyl-1,3a,4,5,6,6a-hexahydro-6a-hydroxy-3-methylcyclopenta[c]pyrazole (2a) was assigned [9].…”